Small diameter welding wire is typically packed in a large container in a single spool which has a natural "cast." This means that in the free state, the wire tends to seek a generally straight line condition. The invention will be described with particular reference to a natural cast type of welding wire stored as a large spool containing convolutions formed into layers of the welding wire. During use, the wire is ultimately payed out from the inside diameter of the spool through the upper portion of a container storing the spool.
When welding automatically or semi-automatically (including robotic welding), it is essential that the large amounts of welding wire be continuously directed to the welding operation in a non-twisted, non-distorted, non-canted condition so that the welding operation is performed uniformly over long periods of time without manual intervention and/or inspection. One of the difficult tasks in such welding is the assurance that the wire fed to the welding operation is fed in a non-twisted or low-twist condition so that the natural tendency of the wire to seek a preordained natural condition will not be detrimental to smooth and uniform welding. To accomplish this task, welding wire is produced to have a natural cast, or low-twist condition. This means that if a portion of the wire were cut into a long length and laid onto a floor, the natural shape assumed by the welding wire would be a generally straight line. This welding wire is wrapped into a spool in a large container (normally a drum) containing several hundred pounds of wire for automatic or semi-automatic welding. The natural tendency of the wire to remain in a straight or non-twisted condition makes the wire somewhat "live" when it is wrapped into the unnatural series of convolutions during placement in the container, resulting in distorting the wire from its natural state. For that reason, there is a tremendous amount of effort directed to the concept of placement of the wire within the container in order that it can be payed out to an automatic or semi-automatic welding operation in a low-twist condition. If the wire is not loaded correctly within the container, massive welding operations, which can consume a large amount of welding wire and a substantial amount of time, can be non-uniform and require expensive reprocessing. This problem must be solved by the manufacturers of welding wire, since they package the welding wire in the large spools which are intended to be payed out for the automatic or semi-automatic welding.
In recent years, there has been a trend toward even larger packages with a larger stock of welding wire. The large packages are intended to reduce the time required for replacement of the supply container at the welding operation. The increased demand for ever-larger supply containers is contrary to and further reduces the ability to smoothly withdraw the welding wire without disturbing the natural flow of the welding wire or twisting the welding wire with adjacent convolutions. Thus, a large volume high capacity storage supply container for welding wire spools must be constructed so that it assures against any catastrophic failure in the feeding of a wire to the welding operation. The pay-out or withdrawing arrangement of the container must be assured that it does not introduce even minor distortions in the free straight flow of the welding wire to the welding operation. The first step in assuring that no minor distortions exist is placement of the welding wire within the container in a manner which will allow withdrawal of the wire from the container in the preferred state.
The welding wire stored in the supply container is in the form of a spool having multiple layers of wire convolutions laid from bottom to top. The inner diameter of the spool is substantially smaller than the diameter of the container. Due to the inherent rigidity of the welding wire itself, the convolutions forming the layers are continuously under the influence of a force which tends to widen the diameter of the convolutions. In order to account for this tendency, the welding wire is laid within the supply container in preferred loop diameters, the loop diameters being smaller than the inner diameter of the supply container. Typically, the loop diameter is at least 15% less than the inner diameter of the drum.
The welding wire is drawn from the manufacturing process and fed over a series of dancer rollers and pulled along by a capstan adjacent the storage container. From the capstan, the welding wire is fed into a rotatable laying head, which is generally a cylindrical tube having an opening at the bottom or along the cylinder adjacent to the bottom. The wire extends through the tube and out the opening, whereupon it is placed into the storage container.
The laying head extends into the storage container and rotates about an axis generally parallel to the axis of the storage container. The wire being fed into the laying head by the capstan is fed at a rotational velocity different than the rotational velocity of the laying head. The ratio between the rotational velocity of the laying head and the rotational velocity of the capstan determines the loop size diameter of the wire within the storage container. As the wire is laid within the storage container, the weight thereof causes the storage container to gradually move downward. As the storage container moves downward, the laying head continues to rotate, thus filling the storage drum to its capacity. The storage drum is incrementally rotated a fraction of one revolution for each full loop of welding wire placed within the storage drum. This causes a tangential portion of the welding wire loop to touch a portion of the inside diameter of the storage container, while the opposite side of the loop is spaced a distance from the side of the container. This is accomplished by moving the laying head off the center line of the storage container by one-half the difference between the loop diameter and the diameter of the storage container.
Accomplishment of this prior art method of loading a storage container is best shown in FIG. 6. This method of loading storage drums with welding wire is important to the effective withdrawal of the welding wire during the welding process. However, as can be seen from FIGS. 7 and 8, this process also results in a loose density packing of the welding wire within the storage container. Depending on the diameter used relative to the storage container, the wire has a higher density along the edge portion of the storage container versus the inside diameter of the spool itself adjacent the spool cavity. This is caused since more wire is placed along the edge portions of the container than is placed along the spool cavity. While the net effect results in welding wire being able to be pulled from the container without substantial problems of tangle or twist, the low density packing means that interruptions in the welding process are more frequent. There is, therefore, greater down time for the welding operation and greater labor costs, since replacement of the supply container at the welding operation and manual intervention in the welding operation is necessary.